Gaztelugatxe is an islet on the coast of the Bay of Biscay belonging to the Biscayan municipality of Bermeo, in the Basque Autonomous Community. It is connected to the mainland by a man-made bridge. On top of the island stands a hermitage named Gaztelugatxeko Doniene in Basque (or San Juan de Gaztelugatxe in Spanish), dedicated to John the Baptist, that late discoveries indicate might date back to the 9th century. With another small neighboring island, Aketx, they form a protected biotope that extends from the town of Bakio to Cape Matxitxako, on the Bay of Biscay.
